It is known to mount substrate. 1 with chip 2 on printed circuit board 3. In compact designs, with a multi-layer ceramic carrier substrates, the discrete components/the chips are mounted on the underside of the substrate between said substrate and the printed circuit board, wherewith heat generated in the components can be transmitted solely to the substrate and from there to the circuit board and its various connections, such as contact pins or beads 4 of solder that melt at high temperatures located between the substrate and the printed circuit board. The connections function as electrical connections and as mechanical spacing means, this latter by virtue of being slightly larger than the remaining discrete components on the underside of the substrate. The components can be shielded by providing on the circuit board, immediately beneath the components, an earth plane 5 which, together with the earth plane of respective components, shields said components without the discrete components being in contact with the earth plane. The substrate-mounted components are liable to generate heat in operation, which in certain cases may be quite considerable. It is therefore important that the thermal contact achieved between the components/the chips and the printed circuit board with its wide copper surfaces is as effective as possible. Because none of the discrete components have direct contact with the circuit board, the major part of the heat generated in said components must be transferred to the circuit board via the substrate and the circuit board connections. In the case of ceramic substrates, the greatest temperature gradient occurs in the longitudinal direction of the substrate in these instances, because ceramics are relatively poor conductors of heat. Transistors in the components may well become damaged at excessively high temperatures, as a result of the poor thermal conductivity of the ceramic substrate.